The almost universally used method for increasing the strength of as-spun synthetic fibers to a significant degree, at least 50%, has been by drawing. For example, strong fibers of polyethylene terephthalate are obtained by extensively drawing the as-spun fiber, e.g., as shown by Boone, et al., U.S. Pat. No. 3,400,194. A technique for increasing the strength of fibers which does not involve drawing is a worthwhile objective.